(a) Technical Field
The present invention relates to a coolant control valve for a fuel cell stack in fuel cell vehicles, and more particularly, to a valve for controlling the temperature of a coolant to flow into a fuel cell stack at an optimum level in order to keep operation of the fuel cell stack stable.
(b) Background Art
In general, a fuel cell stack, being the main power supplier in a fuel cell vehicle, is a device which generates power using, an oxidant (e.g., oxygen in the air) and a reactant (e.g., hydrogen as a fuel). Because a fuel cell stack stably provides an optimum output when a coolant at the optimum temperature flows in the stack, it is very important to keep the coolant, being flowed into the stack at the optimum temperature.
The fuel cell stack usually generates a small amount of heat at the initial stages of fuel cell system. Therefore, when its temperature is low (i.e., below a specification defined value) a coolant flows along a loop of stack to a pump through a coolant control valve and into the stack. As the amount of heat generated by the stack increases and the temperature of the coolant increases over time, the coolant control valve appropriately closes off the bypass loop so that the coolant can flow through another loop from the stack to the pump then through the radiator and the coolant control valve consecutively and then back into the stack.
Considering that the required temperature of a coolant at the inlet of a stack in fuel cell vehicles is about 65° C., a coolant control valve can suitably control the amount that is allowed through each of the loops in response to a signal associated with the inlet temperature of the stack and allows a coolant to flow into the stack, at a constant temperature regardless of the external environment.
A variety of fuel cell systems equipped with a coolant control valve have been proposed in the related art, for example, in Korean Patent Application Publication No. 10-2013-0061445, Korean Patent Application Publication No. 10-2012-0032345, and Korean Patent Application Publication No. 10-2009-0058095.
FIG. 4 is a schematic view showing a coolant control valve for a fuel cell stack in a fuel cell vehicle of the related art. As shown in FIG. 4, the coolant control valve includes a body housing 11 with ports 10a, 10b, and 10c connected to a fuel cell stack, a pump, and a radiator, respectively, a plunger 12 and a plunger shaft 13 disposed in the body housing 11 and selectively opening/closing the ports 10a, 10b, and 10c, an actuator (not shown) disposed in an actuator housing 14 at a side of the plunger 12 and actuating the plunger 12, and a controller 15 controlling the operation of the actuator.
The plunger 12 is rotated by the operation force transmitted through the plunger shaft 13 from the actuator and is operated similarly to that of the related art. Thus, a detailed description of its operation is not provided.
FIGS. 5 and 6 are a perspective view and a cross-sectional view showing parts for sealing the plunger shaft of the coolant control valve for a fuel cell stack in a fuel cell vehicle of the related art. As shown in FIGS. 5 and 6, a aperture 16 through which the plunger shaft is disposed is formed in the actuator housing 14, and a seal 17, a seal washer 18, and a snap ring 19 are sequentially disposed around the plunger shaft 13 in the aperture 16, such that the portion where the plunger shaft is assembled is sealed. In particular, the seal 17 seals the portion in close contact with the circumferential surface of the plunger shaft 13, using a shaft sealing portion 21 that is pushed inward by a tension spring 20 inside the seal 17.
In the coolant control valves for the stacks in most fuel cell vehicles, it is very important to seal the plunger shaft in order to prevent water from flowing into the actuator controller. This is because sealing is directly linked to the components durability under the conditions (e.g., intense cold, intense heat, and large vibration, etc.) in which vehicles are often operated.
However, the sealing of a plunger shaft of the related art is problematic in that water leaks around the shaft within about three to six months of use due to these intense conditions that are generated while vehicles are in motion. For example, water leaks around a plunger shaft due to vapor flowing inside through the contact portion of the plunger shaft and a seal. Additionally, condensation is generated as a result of this vapor in an actuator controller. As such, there is a need to remedy these problems.
Accordingly, the defects of the sealing of a plunger shaft of the related art are as follows. First, the sealing surface of the seal is made of polytetrafluoroethylene (PTFE), so it is vulnerable to heat and cold over time. Second, the plunger shaft is vulnerable to water leakage due to vibration. This is because the restoring ability is low due to the nature of plastic. Third, the sealing ability is reduced due to an increase in wear when pressure is applied, and water leaks through accordingly. Fourth, current shafts are costly to manufacture because they are made up of many parts (e.g., a seal, a seal washer, a snap ring, etc.) required for sealing the plunger shaft.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.